Some kinds of oximino compounds are known as agrochemically or medicinally useful compounds (Patent Documents 1 to 5). In general, oximino compounds have two geometrical isomers, isomers having an E-configuration (hereinafter referred to as E-isomers) and isomers having a Z-configuration [hereinafter referred to as Z-isomers], owing to the presence of an oximino group. It is possible to convert E-isomers to Z-isomers and vice versa or convert either isomers to a mixture of both isomers by known processes. For example, production of a Z-isomer from an E-isomer by light irradiation (Patent Documents 1 and 2), production of a Z-isomer from an E-isomer by treatment with an acidic compound (Patent Document 6), production of an E-isomer from a Z-isomer by treatment with an acidic compound (Patent Documents 4, 5, 7 and 8) and production of a mixture of an E-isomer and a Z-isomer from an E-isomer by light irradiation (Patent Document 3) are known.